1. Field of the Invention
This invention relates to a type of ink jet printing characterized by the discharge of droplets through an orifice of an ink jet printhead that are propelled by bubble generation at an electrically driven heating element in the printhead, and more particularly to a high density, thermal ink jet printhead and process for fabricating it.
2. Description of the Prior Art
In existing thermal ink jet printing, the printhead comprises one or more ink filled channels, such as disclosed in U.S. Pat. No. 4,463,359 to Ayata et al, communicating with a relatively small ink supply chamber at one end and having an orifice at the opposite end, sometimes referred to as a nozzle. A thermal energy generator or heating element, usually a resistor, is located in the channels near the nozzle a predetermined distance therefrom. The resistors are individually addressed with a current pulse to momentarily vaporize the ink and form a bubble which expels an ink droplet. As the bubble grows, the ink bulges from the nozzle and is contained by the surface tension of the ink as a meniscus. As the bubble begins to collapse, the ink still in the channel between the nozzle and bubble starts to move towards the collapsing bubble, causing a volumetric contraction of the ink at the nozzle and resulting in the separation of the bulging ink as a droplet. The acceleration of the ink out of the nozzle while the bubble is growing provides the momentum and velocity of the droplet in a substantially straight line direction towards a recording medium, such as paper.
In U.S. Pat. No. 4,463,359, a thermal ink jet printer is disclosed having one or more ink-filled channels which are replenished by capillary action. A meniscus is formed at each nozzle to prevent ink from weeping therefrom. A resistor or heater is located in each channel at a predetermined distance from the nozzles. Current pulses representative of data signals are applied to the resistors to momentarily vaporize the ink in contact therewith and form a bubble for each current pulse. Ink droplets are expelled from each nozzle by the growth of the bubbles which causes a quantity of ink to bulge from the nozzle and break off into a droplet at the beginning of the bubble collapse. The current pulses are shaped to prevent the meniscus from breaking up and receding too far into the channels, after each droplet is expelled. Various embodiments of linear arrays of thermal ink jet devices are shown such as those haaving staggered linear arrays attached to the top and bottom of a heat sinking substrate and those having different colored inks for multicolored printing. In one embodiment, a resistor is located in the center of a relatively short channel having nozzles at both ends thereof. Another passageway is connected to the open-ended channel and is perpendicular thereto to form a T-shaped structure. Ink is replenished to the open-ended channel from the passageway by capillary action. Thus, when a bubble is formed in the open-ended channel, two different recording mediums may be printed simultaneously.
IBM Technical Disclosure Bulletin, Vol. 21, No. 6, pages 2585-6, dated November 1978 discloses differential etching of mutually perpendicular grooves in opposite surfaces of a (100) oriented silicon wafer. An array of nozzles is formed when the depth of the grooves is equal to one-half of the thickness of the wafer.
An article entitled "Fabrication of Novel Three-Dimensional Microstructures by the Anisotropic Etching of (100) and (110) Silicon" by Ernest Bassous, IEEE Transactions on Electron Devices, Vol. ED-25, No. 10, dated October 1978 discusses the anisotropic etching of single crystal silicon of (100) and (110) orientation and the fabrication of three types of microstructures; viz., (1) a high-precision circular orifice in a thin membrane for use as an ink jet nozzle, (2) a multisocket miniature electrical connector with octohedral cavities suitable for cryogenic applications, and (3) multichannel arrays in (100) and (110) silicon. To make some of these structures, a novel bonding technique to fuse silicon wafers with phosphosilicate glass films was developed. The membrane-type nozzles with circular orifices were fabricated by anisotropic etching of holes in combination with a process which takes advantage of the etch resistance of heavily doped p.sup.+ silicon in the etchant.
U.S. Pat. No. 4,438,191 to Cloutier et al discloses a method of making a monolithic bubble-driven ink jet printhead which eliminates the need for using adhesives to construct multiple parts assemblies. The method provides a layered structure which can be manufactured by standard integrated circuit and printed circuit processing techniques. Basically, the substrate with the bubble generating resistors and individually addressing electrodes have the ink chambers and nozzles formed thereon by standard semiconductor processing.
U.S. Pat. No. 4,335,389 to Y. Shirato et al discloses a liquid droplet ejecting recording head characterized in that the part of the electrothermal transducer contacting the liquid is made of a material which passes a particular weight decreasing test to assure that it will not wear excessively in the operating environment of growing and collapsing bubbles. The cavitational forces produced by rapidly generated and collapsed bubbles, severely erode unprotected heating elements and cause shortened operating lifetimes.
U.S. Pat. No. 4,377,814 to J. R. Debesis discloses corrugated members between adjacent droplet ejecting housings to isolate one from another to prevent cross-talk or the energization of a nozzle in one of the housings other than the selected one.
U.S. Pat. No. 4,417,251 to H. Sugitani discloses a method of manufacturing an ink jet head where the channels which constitute the ink flow path from the reservoir to the nozzles are formed in a layer of photosensitive material placed on a substrate.
Japanese patent application No. 53-122508 to T. Hamano, filed Oct. 6, 1978 and published without examination on Apr. 9, 1980 as Laid-Open No. 55-49274, discloses a fabricating technique for making nozzle plates by producing a mold via anisotropically etching of a single crystalline material to form a plurality of mesas.
Japanese patent application No. 53-122509 to T. Hamono, filed Oct. 6, 1978 and published without examination on Apr. 9, 1980 as Laid-Open No. 55-49275, discloses two single crystalline layers which sandwich therebetween an etching protective layer formed by boron doping of one of the confronting surfaces of the crystalline layers. An identically patterned protective layer is formed on each of the outer surfaces of the crystalline layers. Both of the crystalline layers are anisotropically etched to the center protective layer. The exposed center protective layer is removed and the nozzle plate covered by a protective film to prevent interaction with the ink and the nozzle with orifices at the center protective layer is obtained.